The teen Grammy winner and her brother Finneas O'Connell thrilled fans without show-business flourish in the iHeart Living Room Concert for America.

The teen pop star kept it wonderfully casual on Sunday with her brother Finneas O’Connell to sing her hit “Bad Guy” for the iHeart Living Room Concert for America on Fox. (Watch below.)

The siblings kicked back on their sofa at home in L.A. and performed like there was no one else there, which only accentuated the presentation’s charm.

In introducing the pair for the coronavirus charity concert, host Elton John reassured parents of children now housebound due to the pandemic that home-schooled kids, as Eilish was, can “grow up to win a bunch of Grammys.”

Viewers called the collaboration “effortless” and “cool.”

Love this un-produced acoustic version of Tough Guy, and Billie Eilish seems so stunningly effortless. https://t.co/KDty3vIS62